\[\boxed{\mathbf{16.}}\]
\[16 + 31 = 16 + 30 + 1 =\]
\[= 46 + 1 = 47\]
\[42 + 45 = 42 + 40 + 5 =\]
\[= 82 + 5 = 87\]
\[34 + 62 = 34 + 60 + 2 =\]
\[= 94 + 2 = 96\]
\[83 + 15 = 83 + 10 + 5 =\]
\[= 93 + 5 = 98\]
\[51 + 28 = 51 + 20 + 8 =\]
\[= 71 + 8 = 79\]